22 Jul
2015
22 Jul
'15
8:17 a.m.
On Wed, 22 Jul 2015, tony duell wrote:
Honestly, I've not seen all that many failed 3-terminal voltage regulators
in the field. I've seen some which failed due to insufficient cooling or a
loose heatsink, or with a hole blown in them after being hit with 24V AC,
but not any that have failed short under normal use.
I think he did answer it. If the unit is operating
correctly then the
capacitors must be sufficiently good at that time for that unit.
Now, whether they will go on working is something that is very hard to
tell. But that applies to every other component in the unit. An IC might
work find now and suffer bond-out wire failure later on the same day.
Going purely from the historical data, failures of most semiconductors are
/far/ less frequent than an aluminum electrolytic capacitor (except for a
handful of certain TTL logic, which has been discussed previously here on
classiccmp and elsewhere).
Just like the
NiCd and SLA batteries I mentioned, aluminum electrolytic
capacitors by their very electrochemical nature degrade as they age and
as they are used. You cannot claim that a 20-30 year aluminum
electrolytic
Semiconductors also degrade both with time and use. I would think a
30-year-old 3 terminal regulator IC was also beyond its design life. So
do you replace those 'anyway'? The damage done if one those fails is
likely to greatly exceed the damage done if a capacitor fails. Do you replace all EPROMs in case they develop bit-rot
(They are most
likely way beyond their design life by now)?
I think like most of us on this list, anything I have which is mission
critical gets backed up and can easily be reprogrammed if it fails. Most
of the problems I've seen with bit-rot of EPROMs have been cases where
their quartz windows were not originally covered. I use opaque foil
stickers (I can see if I can find the part number for the stickers I use
if anyone needs it) on any UV erasable memories I program and I haven't
had issues with corrupt data.